This book centres on the transformation that the European Union has undergone in framing its reaction to the Russian aggression towards Ukraine, and analyses the effects that that reaction is having across a number of its policies. Key EU policy domains examined include the formulation of sanctions packages under the Common Foreign and Security Policy (CFSP) and their implementation and enforcement, but also migration, enlargement and defence policy. The volume presents a legal analysis of the innovations introduced in various policy fields and their profound implications on EU external action writ large, including a discussion of ensuing case law of the Court of Justice of the European Union and the impact of the EU practice on restrictive measures on Public International Law. The book provides an updated examination of the latest developments regarding the EU’s reaction to the Russo-Ukrainian war and their legal and political implications. It will be of interest to scholars of European Law, European studies, International Relations and Political Science, in addition to foreign policy practitioners and legal professionals. Sara Poli is full Professor of EU law in the Department of Political Science at the University of Pisa in Italy. Madalina Moraru is an Associate Professor of EU Law in the Department of Political and Social Sciences of the University of Bologna in Italy. Luca Paladini is an Associate Professor of EU Law in the Department of Humanities of the University for Foreigners of Siena in Italy. Clara Portela is a Professor of Political Science in the Department of Constitutional Law and Political Science of the University of Valencia Faculty of Law in Spain.